The subject matter disclosed herein relates to digital radiography (DR) imaging, in particular, to long-length imaging that requires multiple DR detectors.
Special cassettes and films of extended length are sometimes used when imaging a long segment of a subject, such as a human body, with an analog screen-film technique. An x-ray source and the cassette are both centered to the subject to be examined and an x-ray collimator is adjusted to cover the imaging area, whereby a single x-ray exposure is performed. Flat-panel DR detectors are usually limited to 43 cm in length. For long-length imaging applications this would require separate exposures to be taken at different regions of the subject. In order to create a large, single composite image for diagnosis, the individually captured images of the subject need to be stitched together using digital computer-implemented reconstruction techniques.
Two primary approaches are available to acquire long-length imaging exams with flat-panel detectors. In both methods, the detector moves from one imaging position to the next behind the subject. In one known embodiment, the x-ray energy source moves (rotates or tilts) in order to track and expose the detector. In this x-ray source tilting method, the central x-ray pointing direction varies from one exposure position to the next to deliver the x-rays to the detector. In another known embodiment, the x-ray source focal spot position is not stationary, but translates synchronously with the DR detector parallel to the detector's axis of travel.
There are advantages to both embodiments. For example, the tilt method is free of parallax artifacts inherent in the x-ray source translation method. Because of parallax distortion, the geometric integrity of the subject's features in the stitched image may be degraded, particularly in the stitch overlap regions. Automatic image stitching can be achieved with high geometric accuracy such as provided by the Carestream DR DirectView Long-Length Imaging System. A high-precision hardware encoder reports the exact detector travel distance between exposures. In a direction transverse to the detector motion axis, software automatically analyzes the subject's features in the overlap regions to find the best alignment between any two adjacent images. The total stitch error has been demonstrated to be small under stringent exposure conditions.
Automatic exposure control can be used during the long-length imaging exams in order to apply just the right amount of exposure to each region of the subject for image quality. Software may also automatically adjust exposure discrepancies and compensate for the latitude differences, therefore providing optimized image presentation for each image. The image-processing reconstruction algorithm stitches together the individually optimized, display-presentation-ready images to create a smooth and seamless composite single image for diagnosis. The seam line between any two images may be blended without any visible artifacts during this digital process. Such imaging software should be able to adjust and fine-tune stitch positions to compensate for movement of the subject during the exam to avoid exposure retakes. In all of the examples just described, it would be advantageous if multiple DR detectors could be used to simultaneously capture a composite radiographic image of a subject in a single exposure.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.